1. Field of the Invention
The present invention pertains to a method and apparatus including an unbuffered oscillator for generating microwave frequency range radiation for measuring the composition of water-oil and other mixtures of matter and, in particular, wherein the mixture comprises a relatively high concentration of water in a water-oil mixture.
2. Background
The above-referenced patent application describes a microwave-based apparatus for measuring the concentration of one liquid in another, particularly relatively low concentrations of water in oil. In the production and transportation of crude oil, for example, it is important to be able to determine the amount of water mixed with the crude oil, which is often present as naturally-produced water or water which has become mixed with the oil as a result of certain reservoir stimulation processes. In some instances relatively high percentages of water in oil occur as a result of producing from formations which have a so-called "high water cut". In many crude oil reservoirs, the percentage of water in the produced liquid mixture may easily exceed 50% and go as high as 80% or 90%, at least at various times in the production process.
The apparatus described in application Ser. No. 06/932,868 provides an unbuffered or unisolated, free-running oscillator circuit which is connected to a fluid measurement section having a coaxial transmission path comprising a conduit having a center conductor extending through the conduit and wherein the conduit itself forms a part of the conductive path or circuit. The apparatus is capable of detecting a change in operating frequency of the oscillator as a function of the change of the composition of the liquid mixture being conducted through the conduit of the measurement section. In particular, the apparatus is utilized to determine the change in percentage of water contained in the oil flowstream and at relatively low percentages (less than 5% to 10%) of water in oil, wherein the water exists as dispersed droplets, a water-in-oil emulsion.
For relatively low percentages of water in oil the change in the oscillator circuit operating frequency can be easily measured and compared to an pre-established relationship between oscillator operating frequency and the composition of the water-in-oil mixture to determine the water content. However, when the water content of the composition increases to about 50% to 86%, by volume, the mixture becomes inverted to an oil-in-water emulsion and apparatus with a metal center conductor and a metal outer conductor/conduit in direct contact with the mixture being measured undergoes a loss in field intensity due to a short circuit between the conductor elements. This occurrence renders the aforementioned apparatus essentially incapable of measuring the water content of the composition.
However, in accordance with the present invention an apparatus which includes a center conductor as described herein and the practice of the improved method of determining the composition of a material, which includes measuring power loss of microwave radiation being propagated through the apparatus, can be used to determine the water content of a liquid mixture or composition having a relatively high percentage of water, including an oil-in-water emulsion.